A data centre is a late 20th Century development that has grown as a response to the increasing demand for computer processing capability and a recognition of the importance of information technology (IT) in the place of every business and organisation today. Whereas smaller organisations have sufficient processing power with laptops, PCs and occasionally servers, larger organisations require higher capacity centralised processing to serve a wide range of needs and applications. A few years ago this capacity was supplied by large mainframe computers, but more recently the method used has been to provide data centres comprising many networked computer servers known as “blades” installed in racks enabling controlled and modular expansion of capacity. The racks also typically house storage systems and/or telecommunications equipment such as routers to handle data flow between the computer servers and data flow between the data centre and the outside world.
One key problem faced is how to cool a data centre effectively and efficiently. It will be appreciated that data centre facilities are of critical importance to their users, and so overheating of servers (which is likely to cause the server to temporarily or even permanently fail) must be avoided.
One method of the prior art, now recognised to be inefficient, is to provide a room in which air-conditioning units (mechanical DX coolers) flood the room with chilled air (by drawing air from the room, chilling it, and then pumping the chilled air so produced back into the room) so as to provide a reservoir of chilled air from which the servers may draw cooling air by means of their internal fans. No entrainment of cooling air is provided.
In another data centre arrangement of the prior art, the racks are laid out in rows. Cooling is provided by direct expansion (DX) or chilled water cooling plants. The cool air produced by these units is entrained through an underfloor plenum and exits through floor grilles at the front of the IT rack rows. The IT products installed in the racks contain integral fans which draw the cooled air from the front across the circuitry and heat is exhausted via vents in the products to the rear.
A typical version of the prior art arrangement utilising under-floor cooling and racks in rows, is shown schematically in FIG. 1 of the attached drawings. Thus, the data centre includes a rack room 1 defined by walls 2 in which two sets of racks 4 for IT equipment are accommodated. The IT equipment in the racks 4 generate heat, represented by arrows 6. The cooling of the IT equipment is achieved by introducing cold air, via a floor void, into the room by means of air conditioning units, the cold air being represented by arrows 8.
The drive for more efficient use of power has given rise to a need to make the cooling regimes used in data centres more efficient, as cooling of equipment typically contributes significantly to the power used by a data centre. For example, the power usage in certain data centres may require between 1 kW and 2 kW of power for every 1 kW of power used to power the IT equipment, a significant proportion of which would be related to cooling.
In certain arrangements of the prior art, the separation between IT racks creates a ‘hot aisle’ into which air is expelled by the IT products in the racks and a ‘cold aisle’ from which cooler air is drawn into and through the IT products by their integral fans. In such arrangements, it is important to maintain a controlled air flow so that no ‘hot spots’ are created within the rack room where overheating servers are not in fluid communication with cooling air. One method of avoiding this problem is to supply significantly more cold air than the servers actually need at any given time and ensuring that the required amount of cooling air is provided to every server in the rack room.
Typically, cooling air is transported from the cooling plant to the racks via duct work and/or an underfloor plenum, both of which add significant resistance to air flow. In order to supply the large volumes of cooling air required to ensure that each and every server is supplied with an adequate amount of cooling air, the cooling air has to travel at high velocity through the duct work and/or the underfloor plenum. Typically, large, powerful fans are used to drive the cooling air from the cooling plant to the servers. When air is supplied to a cold aisle via duct work and/or an underfloor plenum at high velocity, it can be difficult to ensure that each and every server in the cold aisle is effectively cooled. For example, servers located close to the point at which high velocity cooling air enters the cold aisle are often bypassed by the cooling air stream because the integral server fans are not powerful enough to redirect the cooling air and draw the air across the server effectively. One approach to reducing the velocity of the cooling air (whilst maintaining adequate cooling) is to lower the temperature of the cooling air by increasing the amount of mechanical cooling. However, reducing the temperature of the cooling air is an energy intensive process that reduces the efficiency of the data centre.
One approach to improving the efficiency of data centre cooling is to utilise ambient outside air in addition to or instead of mechanically cooled air. Often, in data centre cooling methods utilising cooling air comprising ambient air, the temperature of the cooling air is higher than in cooling methods utilising cooling air consisting of mechanically cooled air. Typically, to achieve adequate cooling using higher temperature cooling air, the airflow across the servers needs to be higher, and so even larger volumes of cooling air need to be supplied to the cold aisles. WO2010/139919, WO2011/073668, WO2011/148175 and WO2010/139921 disclose methods of utilising ambient air from outside a data centre to cool items of electronic equipment in which cooling air is transported to the cold aisles via an access corridor, thus providing a relatively low resistance path via which large volumes of cooling air can be transported to the cold aisles at low velocity. To ensure that the servers are provided with an adequate amount of cooling air, those methods utilise large fans upstream of the servers to maintain a positive pressure of cooling air in the cold aisles relative to the pressure of the hot air in the hot aisles.
In general, known methods of cooling data centre buildings having a controlled air supply path with hot and cold aisle separation, the methods comprising the use of ambient air (optionally with filtration of the air), mechanically cooled air (for example using direct expansion or chilled water cooling plants), and/or humidification/dehumidification of cooling air, utilise banks of fans, individual large fans, and/or cooling equipment comprising large integral fans.
Although considered necessary to ensure adequate and reliable cooling, the operation of large central fan arrangements accounts for a significant proportion of a data centre's energy usage. Furthermore, such central fan arrangements can become a single point of failure for the data centre. For example, should a fault develop with a central fan arrangement, the entire data centre might be forced offline. Additionally, during operation, large fan banks produce undesirable levels of noise. Often, sound attenuation equipment is used to reduce the volume of the fan noise transmitted to other parts of the data centre, for example personnel corridors and server rooms, and its surroundings. Such sound attenuation equipment adds to the construction and maintenance cost of the data centre, and adds resistance to the air flow path in turn necessitating the use of stronger fans and leading to an increase in operational costs.
A small number of methods use convection to draw cooling air through a data centre building as an alternative to using central banks of fans. In such methods, hot air rises through high level chimneys and or roof ridge vents, with assistance from the prevailing wind to draw air out of the top of the building and to push ambient air into a lower part of the building through external wall vents. A drawback of such designs is that they require careful planning and siting since their utility is dependent on finding an appropriate location. The limited number of suitable locations and the requirement to design each new data centre individually significantly reduces the flexibility of such methods.
The present invention seeks to provide an improved method and apparatus for cooling a data centre. Alternatively or additionally, the present invention seeks to provide a system for cooling a data centre that mitigates one or more of the above mentioned disadvantages.